Abstract Book

S1107

ESTRO 37

5 Istituto Europeo di Oncologia and University of Milan, Division of Radiation Oncology and Department of Oncology and Hemato-oncology, Milano, Italy 6 Istituto Europeo di Oncologia, Unit of Medical Physics- European Institute, Milano, Italy 7 University of Milan and Istituto Europeo di Oncologia, Department of Oncology and Hemato-oncology and Department of Medical Imaging and Radiation Sciences, Milano, Italy 8 Politecnico di Milano and Centro Nazionale di Adroterapia Oncologica, Dipartimento di Elettronica Informazione e Bioingegneria and Bioengineering unit, Milano and Pavia, Italy Purpose or Objective Lung Optimized Treatment (LOT) is an innovative CyberKnife procedure that provides three fiducial-less motion management approaches. In 2-view (2V) the tumor is visible in both orthogonal X-ray images and full motion tracking is performed. In 1-view (1V) the tumor is visible in a single X-ray image, therefore motion tracking is combined with an internal target volume (ITV)-based margin expansion. In 0-view (0V) the lesion is not visible, consequently the treatment relies entirely on an ITV- based approach. The aim of the study is the evaluation of target coverage in the above-mentioned modalities. Material and Methods We analyzed data of 30 patients treated with LOT from November 2014 to February 2017 at Radiotherapy Division of European Institute of Oncology (Milan, Italy). Only 2V patients were selected since they provide comprehensive information on the three-dimensional tumor motion in correspondence to each X-ray image. Treatments in 1V and 0V modalities were simulated from these data by processing log files and planning volumes. In our Institution, planning target volume (PTV) margins are defined according to the tracking modality: end- exhale clinical target volume (CTV) +3mm in 2V and ITV + 5mm in 0V. In the 1V scenario, the ITV encompasses only tumor motion along the non-visible direction. Then, non- uniform ITV to PTV margins are applied: 3 mm and 5 mm in the visible and non-visible direction, respectively. CTV and PTV positions were derived from treatment log files according to the specific tracking modality. Then, a coverage measure was calculated as the intersection between CTV and PTV volumes in correspondence to each image acquired during irradiation. Similarly to dose- volume histogram, CTV coverage-volume histograms are derived for each patient and treatment modality. Results In Fig.1, the coverage-volume histogram curves report the Y% of the CTV that is within the PTV in at least X% of control images acquired during treatment. The coverage of the 95% of the CTV is defined as C95%. The median values of C95% among the patient population are comparable for the three tracking modalities and larger than 98.1%.

Material and Methods The breast radiotherapy is driven with the help of a spirometer and video feed back assisting the patient to provide a deep inspiration breath hold during each imaging and delivery phase. The heart position was measured on the portal images compared to the DRR. The study contained 98 portal images of 15 patients having each three successive and weekly imaging controls. We defined three measurements with the heart image, the ribs and the inferior breast gland limit. One measurement was defined in the middle head-feet heart distance. The second was at the inferior breast gland limit and a third position was feet direction with the same gap of the two first positions.

Results The measurements were obtained with the graphic rule on a stretched image area over the entire screen. The manual use of the graphic rule was evaluated with a potential error of less than 2mm due to the mouse tool and the blurred edge of each anatomy image.The mean / maximum heart position variation in the middle heart head-feet image was 0,36 / 0,51 cm. At the inferior breast gland limit we measured 0,32 / 0,52 cm and on the third position feet direction 0,30 / 0,58 cm. Some cine images were acquired with the objective to evaluate the intra-Breath-Hold movement but we could not highlight credible results inside 2 mm as read in some articles. Conclusion The heart position reproducibility during spirometric DIBH radiotherapy is fully acceptable. These results can be used to take into account the dosimetric effect in the dose gradient area on the heart edge. However, only the maximum dose can be evaluated as the mean dose would need a CB-CT and a deformable heart image process. R. Ricotti 1 , M. Seregni 2 , D. Ciardo 3 , S. Vigorito 4 , E. Rondi 4 , G. Piperno 3 , M.A. Zerella 5 , S. Arculeo 5 , C. Francia 5 , D. Sibio 5 , F. Cattani 6 , R. Orecchia 7 , M. Riboldi 2 , G. Baroni 8 , B. Jereczek-Fossa 5 1 Istituto Europeo di Oncologia, Radiotherapy Division, Milano, Italy 2 Politecnico di Milano, Dipartimento di Elettronica Informazione e Bioingegneria, Milano, Italy 3 Istituto Europeo di Oncologia, Division of Radiation Oncology, Milano, Italy 4 Istituto Europeo di Oncologia, Unit of Medical Physics, Milano, Italy EP-2027 Evaluation of target coverage in lung stereotactic radiotherapy with Cyberknife system

Conclusion PTV margins are adequate to compensate tracking errors and tumor motion in all LOT treatment modalities. Since stereotactic body radiotherapy ensures high dose